Patent GB-668064-A (GB)
Title: Improvements in or relating to coilers for reversing hot mills
IPC: C21D9/68
Filed: 1948-05-31
Abstract: 668,064. Control of several motors; electromagnetic switches. MONTGOMERY, A. B. May 31, 1948. No. 14651/48. Classes 38 (iii) and 38 (v). [Also in Group XXII] Motor control systems. Relates to a reversing rolling mill for metal strip in which coiling drums are located on each side of the mill stand and in which separate motors drive (a) the rolls, (b) each drum, and (c) guide and coiler rollers associated with each drum and consists in an automatic control system whereby on each reversal a constant rolling speed is obtained with constant forward and back tensions applied to the strip. At each reversal a further motor brings guides on the rotating side of the press into operation and removes the guides on the exit side. The main motor MM is driven by a motor generator MG and motors RRM, RCM, LRM and LCM for the right and left coilers and associated parts are driven by motor generators RG, LG. The motor MM is coupled to the constantly excited field exciter PE which thus generates a voltage proportional to the speed of that motor, and supplies the main field windings RGmf, LFmf of the generators RG, LG so that these generators have polarity and voltage depending on the direction and speed of rotation of the main rolls 14, and the coilers and their associated rollers are correspondingly driven, when the contacts LSC3 &c. are closed and the contacts LSC1 &c. open. With the reverse arrangement the coiler &c. motors are dynamically braked. In the initial stages the partly rolled strip is passed backwards and forwards through the rolls 16 without coiling. Control is exercised by operators in pulpits located to the left and right of the mill. Assuming that the strip is on the right of the mill it will engage the right hand flag switch RF, maintaining its contacts 1, 2, 3 closed. Trigger switches LT, RT are in their lower position, their contacts 1, 5, 6 being open and 2, 3, 4 closed. The operator in the left pulpit moves his master switch in the direction to close contacts LMSl1 and 2. A circuit is made from the line L1 via LMSl1, LT2, the solenoid of relay switch CL contacts CR10 of relay switch CR, and the contacts E2 of the emergency stop switch E to the line L2. Switch CL is thus operated to close contacts 2 to 7 and 10, 11, 12 and open contacts 1, 8, 8a and 9. This movement is controlled by a dash pot and the switch rod is connected to operate a rheostat FR1 in the circuit of the main generator field MGf, to reduce the resistance. The dash pot allows the switch rod to move rapidly in the opposite direction. The opening of CL1 and closing of CL2 stops dynamic braking and connects the main motor armature to the main generator ; at the same time contacts CL3 and 4 energize MGf, which strengthens as FR1 decreases, in the direction to cause the mill rolls to roll from right to left. Contacts CL6 and 7 complete the armature circuit of a guide adjusting motor which closes the guides on the feed side and widens them on the delivery side. A limit switch stops the motor on completion of the movement. Opening of the contacts CL9 prevents the closure of the circuit through the solenoid of the relay CR so that CR is locked during the operation of CL. Closing of the contacts CL11 energizes the solenoid of the relay LSC through the contacts LT4 and LRLS in parallel, and also the solenoid of the relay RSC through RT4 and RRLS. Opening of the contacts LSC1, 2 and closing of LSC3, 4 disconnects dynamic braking and connects the armatures of LCM and LRM to the generator LG, whilst closing of the contacts LSC5 energizes the main field of the generator LG from the pilot exciter PE. The relay RSC acts in similar manner for the generator RG and its associated motors. Closing of contacts CL5 energizes the compensating fields LGcf, RGcf of the generators LG, RG. Since the polarity of the pilot exciter reverses when the main motor reverses, whereas that of the compensating fields remains constant, one of these fields augments its main field whilst the other diminishes it. In this way the speed of the. guide rollers and the coiler on the delivery side of the mill is maintained higher than that on the feed side, regardless of the direction in which the mill is running. When the strip has passed through the rolls 14 the operator moves the master switch LMS to neutral position whereby the motors MM, LCM, LRM, RCM and RRM are all switched out and dynamically braked. If a further pass is required without coiling either LMS is moved to close contacts LMSr or RMS is moved to close contacts RMSr. The strip will have contacted flag switch LF and closed the contacts LF1, 2 and 3. Relay switch CR closes and the main generator field is energized with reverse polarity through contacts CR3 and 4. The rolls and also the pilot exciter are now driven in the reverse direction and consequently the motors LCM, LRM, RCM and RRM are reversed also. The guide adjusting motor GAM, Fig. 10 (not shown), again has a brief run to reverse the arrangement of the guides. When the strip has elongated sufficiently to require coiling, e.g. on its next passage from right to left, the operator raises the trigger switch LT closing contacts LT1, 5 and 6 and opening contacts 2, 3 and 4. Closing of LT1 prepares a circuit through the contacts CL10, at present open, closing of LT5 prepares a circuit through contacts LF3, also open, and closing of LT6 energizes a circuit from the line L1 through the solenoid VL and the normally closed contacts TL2 and TR2 to the line L2. This opens a valve admitting fluid to raise the left hand roller 56 into contact with the coiling drum 18. The switch LMS is now moved to close the contacts LMSl 1 and 2. Closing of LMSl1 completes a circuit through RF1, solenoid of CL, and contacts CR10 and E2. Operation of the switch CL then starts the main motor MM and the auxiliary motors as described above. The motor LRM rotates the coiler drum 18 until a slot therein is in line with a deflector guide raised with the roller 56, when a limit switch LRLS opens. Since contacts LT4 and LT1 are open the relay LSC is de-energized and the motors LRM and LCM are stopped. The switch LRLS only opens during clockwise rotation of its drum. As the end of the strip emerges from the rolls 14 it operates flag switch LF to close its contacts LF1, 2 and 3 and passes into the coiler drum through the slot. Closing of LF3 completes a circuit through LT5, CL12 and the solenoid of the relay TL, closing contacts TL1 and opening TL2. Closing of TL1 bypasses RRLS (the limit switch for the right hand coiler drum) and completes a circuit through CL11 to operate the relay LSC and start the motors LCM and LRM to coil the strip. Opening of TL2, after a time lag due to the discharge of the condenser VLC, opens the valve and allows the left hand roller 56 to descend. The operator now closes switch LLM, Fig. 8, to operate the relay RSL closing its contacts RSL1 and 2, and also switching resistance FR2 into the field circuit MMf and cutting resistance FR3 out of the compensating fields LGcf and RGcf of the generators LG, RG. This speeds up the motors to increase the rolling speed. Contacts RSL2 act to close a holding circuit for the switch LLM. During this time the right trigger switch RT is raised making preparatory changes in the circuits. As the end of the strip approaches the rolls, the operator moves the switch LMS into neutral causing the motors to slow down and run at the initial speed under control of the flag switch RF, and when the end of the strip passes this switch all the motors are stopped. On the next reverse closing of the master switch the strip uncoils from the left drum and is wound on the right coiling drum, and so on until the desired reduction is attained. A switch, not shown, provides for energizing the solenoid of the emergency relay switch E at any time breaking the control circuits at E1, 2 3 and 4 and stopping all the motors. In order to vary the back and front rolling tensions regulators TR1, TR2, TR3 and TR4, all of similar construction, are provided in the armature circuits of the motors LCM, RCM, LRM and RRM respectively. The regulator TR1, Fig. 11, comprises a pair of speed series coils 200, 202 connected at a1, a2, Figs. 7 and 11, in the'armature circuit of the motor LCM. A rotatable coil 204, between these coils, is in series with a high value variable resistance R1, the whole being shunted across the armature terminals al, a3. Movement of the coil 204 is opposed by a spring and the coil takes up a position corresponding to the power input of the motor irrespective of what the applied voltage may be. As the coil moves it operates a variable resistance 208 in the field circuit LCMf of the motor LCM. When power is being supplied to the motor the contacts CL8 will be closed and the resistance FR4 is shorted out. When rolling from left to right the speed of the motor LCM would be too slow and the resistance FR6 is then operative to weaken the field and bring up the speed. Since the motor LCM is designed to operate at a constant speed the use of the regulator TR1 is precautionary only and the regulator does not come into action unless some abnormality in the operation of the mill arises. The regulator TR3 controlling the speed of the drum driving motor LRM functions to take care of the variation introduced by the increase of the effective diameter of the drum as the strip is wound thereon. Regulators TR2 and TR4 act similarly to TR1 and TR3. Instead of effecting the control from the left pulpit the right pulpit may be used or the control may be divided between the two. The relays CL and CR are mutually interlocked by the controls CR10 and CL9 so that only one can be in operation at any one time. Should the strip move so far that both flag switches are out of action, switches MIL, MIR, Fig. 8, provide a manual inching control. Electromagnetic switches. The relay switches CL, CR, Fig. 9, have the contactors 102 mounted on rods 90 raised by solenoids 94 retard